The technical field of this invention is a vehicle suspension control system.
Many automotive vehicles have suspensions that vary damping force in response to control commands determined by a computer controller, in order to improve overall vehicle ride comfort and handling. One such system is responsive to absolute body modal velocities derived from relative body/wheel position or velocity sensors and acts through controllable dampers to provide control of sensed body motions and reduce ride harshness. This control also provides a measure of wheel control; but it is generally designed for a balanced approach between comfort and handling.
When a vehicle having such a suspension control is subjected to vehicle handling events that affect vehicle body motion, it is sometimes desirable to provide an enhancement to the normal suspension control to counteract the body motions caused by the events. This is true for some vehicle handling maneuvers such as turning, which tends to induce body roll, and braking or acceleration, which tend to induce body dive or lift; and it is also true for the action of some vehicle handling control systems, such as a yaw rate correcting system, which can induce vehicle body motion due to selected application of individual wheel brakes.
The related applications listed above describe examples of such systems that provide a basic suspension control of the semi-active xe2x80x9cskyhookxe2x80x9d type responsive to relative body/wheel velocity at the corners of the vehicle body to derive a demand force command for each of the dampers for vehicle body control and apply each of the derived demand force commands to its respective damper only when a comparison of the direction of the demand force command with the sensed relative velocity of the damper indicates that a force corresponding to the demand force command can be effectively exerted by the damper. The latter requirement is due to the fact that a damper can only apply a damping or restraining force and can thus only help control body motion when the damper assists the associated wheel assembly in exerting a force in the required direction on the associated corner of the vehicle body.
The systems also each provide an additional enhancement to the basic xe2x80x9cskyhookxe2x80x9d control which is responsive to a signal indicative of a predetermined vehicle handling maneuver or control action that tends to produce a predictable vehicle body motion to determine, independently of the vehicle body control, enhanced body control damping commands to be supplied to selected wheels to counteract the specific predicted motion. These enhanced body damping commands are applied essentially in an over-ride mode, without regard for the direction of demand force for the particular suspension damper or damper affected. The algorithms described in the applications provide for separate levels of damping to be applied to front and rear dampers and to allow selected dampers to be controlled in compression only, rebound only, both or neither. The result of these controls is a beneficial improvement in handling and control, somewhat at the expense of ride comfort during the times when the enhanced damping commands are in effect.
The method and apparatus of this invention provide a greater dimension of suspension control with respect to ride comfort in the application of the systems described above, by providing the ability to vary the enhanced body damping commands at individual corners of the vehicle in response to the direction (compression, rebound) and/or magnitude of the relative velocity of the damper to which the enhanced body damping command is to be applied.
The control described above is modified in that a first value is derived from one or more measured vehicle dynamic variables associated with a sensed vehicle handling event, and a body control enhancement damping command is derived from the first value modified in magnitude in response to at least one of the direction and magnitude of the sensed relative velocity of damper to which the body control enhancement damping command is to be applied. In one aspect of the invention, predetermined compression and rebound values are stored for each of the corners of the vehicle, one of the predetermined compression and rebound values is selected according to the direction of the sensed relative velocity of the damper to which the body control enhancement damping command is to be applied, and the body control enhancement damping command is derived from the first value modified in magnitude in response to the selected one of the predetermined compression and rebound values. In another aspect of the invention, a magnitude of the sensed relative velocity of the damper to which the body control enhancement damping command is to be applied is determined and the body control enhancement damping command is derived from the first value modified in magnitude in response to the magnitude of the sensed relative velocity of the damper to which the body control enhancement damping command is to be applied. Yet another aspect of the invention modifies the magnitude of the body control enhancement damping command in response to both the direction and magnitude of the relative velocity of the damper to which the body control enhancement damping command is to be applied, as described in the previous two aspects of the invention.